Large diameter casing and piling, being assembled and installed in a vertical orientation, may be handled by drilling rigs but are often handled by site preparation rigs having less capacity for lifting and for supporting rig floor loads.
Slip bowls designed to handle large diameter tubulars have been directed to short term use. For short term use, efficiency essential to drilling spiders, is rarely present. Large oil field tubulars may be six feet in diameter and a spider based on the usual drilling rig spider would be very large and heavy. Site preparation rigs would rarely be capable of handling such massive spiders. Such massive spiders would take up excessive rig floor space and alternatives are preferred.
Throughout the early rotary drilling history the slip set could be manually lifted out of the slip bowl of the rotary table and placed upon the nearby horizontal surface. For stability, at rest, the hingedly connected slip set is left slightly curved. When needed, one person can drag the slip set into the slip bowl to embrace the drill string, which it will then support when necessary.
The term spider applies to slip bowls, slips, and powered slip manipulation gear. The term apparently originated when larger pipe was run into wells and the rotary slip bowl could not be used. The large pipe adaptation sat on the rig floor above the rotary table.
More modern spiders in drilling service are fluid powered with the operating mechanism enclosed for safety. Efficient and safe handling of drilling-type slips have been achieved. For the slip bowls used on rather large oil field tubing, slip handling is beyond the capacity of human lifting and rig service hoisting gear is used. The individual slip elements are much like the drilling related slips but the large pipe periphery calls for slips made up into chains that may contain over thirty slips. When rig supplied hoists are used to lift slips, the slip chain becomes unruly once clear of the confining slip bowl. Some man-handling of the slip chain is necessary. That activity is hazardous and it is always relatively slow. Cost and danger supplies incentive to better manage the slips used on large tubulars.
A spider normally includes a slip bowl and the slip operating machinery. When very large pipe is involved, the spider definition is not satisfactory and there is usually no rotary table to contain a slip bowl. A large slip bowl is provided by an inner surface of a large ring and a slip chain is made up of hingedly connected individual slips. The slip chain may be handled by many men or rig hoists. The apparatus herein disclosed can be considered to be that required, in conjunction with slips and the slip bowl, to comprise a spider.